Cholesteatomas are benign growths typically arising in the outer and middle ears. These fairly common lesions represent a dysregulation of skin growth and cause localized temporal bone destruction. Cholesteatomas commonly cause chronic infection and often lead to hearing loss, dizziness or facial nerve paralysis. Complications of cholesteatoma include serious conditions such as meningitis and brain abscesses. There are no medical therapies for cholesteatoma and current treatment is surgical resection. Recurrences are common and most individuals with cholesteatoma will undergo multiple operations. The long-term goal of this study is to identify the mechanisms regulating cholesteatoma growth for the development of novel pharmacological treatments for this disorder. The relatively easy access of the middle ear to intratympanic drug delivery makes a topical inhibitor of cholesteatoma growth an attractive mode of primary or adjunctive therapy. Recent studies have shown that benign and malignant tumor growth is associated with alterations in human microRNA expression and activity. Although phylogenetically ancient, microRNAs have only recently been identified as potent regulators of protein translation. These small nucleotides (~22nt) bind to messenger RNA (mRNA) and down-regulate protein production by degrading the message or by blocking translation. Our preliminary studies show significant up-regulation of human microRNA-21 (hsa-mir-21) in cholesteatoma as compared to normal post-auricular skin. Hsa-mir-21 is up-regulated in many tumors including vestibular schwannoma, hepatocellular carcinoma and breast cancer. This microRNA is predicted to target PTEN, PDCD4 and TPM1 messenger RNA and to be regulated by STAT3. These proteins are involved in cell growth and tumor suppressor pathways. Using real-time RT-PCR, western blot analyses, and in situ hybridization we will explore the role of hsa-mir-21 in regulating cholesteatoma growth. Further, we will investigate the role of additional microRNAs in this disorder by high-throughput microRNA microarrays. A cell culture system will also be developed to test the potential of specific microRNA interfering molecules to inhibit cholesteatoma growth and proliferation. PUBLIC HEALTH RELEVANCE: Cholesteatomas are aggressive but benign lesions of the ear that commonly cause hearing loss and chronic infections. There are no medical treatments and repeated surgeries for removal are common in children and adults. This study seeks to identify novel regulators of cholesteatoma growth that may lead to pharmacological therapies and thus improve hearing outcomes and avoid serious medical and surgical complications.